1. Field of Invention
The present invention relates generally to the field of file system access and manipulation. More specifically, the present invention is related to maintaining files while they are open or in use.
2. Discussion of Prior Art
One of the greatest characteristics of current electronic and magnetic storage media and systems is the ease and speed with which changes can be accomplished. File systems having hundreds, even thousands, of files are easily updated to reflect minor or major changes through standard interactions between user applications and modern operating systems.
One area where this ability is greatly utilized is client/server applications in which a server application provides access to or data from files which are frequently updated. In this environment, the data rapidly fluctuates and the server application""s accuracy and usefulness depend on its ability to provide the most up-to-date information without errors.
The prior art has failed to adequately address the issues and difficulties of updating files while simultaneously providing access to those files. If a file is updated while a user is accessing it, then the user may receive inaccurate data (garbage) or find themselves in an inoperative processing environment (hung application). The common prior art methods of addressing this problem include 1) stopping the server application, updating a file and then restarting the server application or 2) storing the updated file in a temporary location and whenever the server application restarts, replacing the out-of-date file.
While these prior art solutions do prevent conflicts from occurring when updating files which are being accessed, they require a stop and restart of the server application to accomplish their goal.
Whatever the precise merits, features and advantages of the prior art, it fails to achieve or fulfill the purposes of the present invention. In particular, the prior art does not provide for a file update method which allows access to an updated file while concurrently preserving open connections to a previous version of the file, all without a system or application restart.
A master site maintains up-to-date copies of files which it provides to a number of mirror sites. Each mirror site is responsible for receiving the file updates and integrating them while continuing to provide service to those and other files (FIG. 1a). The invention involves temporarily storing an updated file, moving it to an intermediate location, redirecting calls to the out-of-date file to the intermediate location, and moving the intermediate file to its permanent location when user activity permits (FIG. 1b). Of particular importance is the redirection of file accesses by using a monitoring program to inject substitute operating system (OS) library calls into the running application which handle calls to the out-of-date file version.